Biological Weed Control Technology - ACS Symposium Series (ACS

Chapter 19

Biological Weed Control Technology An Overview 1

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Ν. E. Rees , P. C. Quimby , and J. R. Coulson

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Range Weeds and Cereals Research Unit, Agricultural Research Service, U.S. Department of Agriculture, Montana State University, Bozeman, MT 59717-0056 Insect Biocontrol Laboratory, Biological Control Documentation Center, Agricultural Research Service, U.S. Department of Agriculture, Building 004, Room 3, BARC-West, Beltsville, MD 20705

Downloaded by UNIV LAVAL on July 13, 2016 | http://pubs.acs.org Publication Date: May 5, 1995 | doi: 10.1021/bk-1995-0595.ch019

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An overview is presented describing the procedures used by USDA, Agriculture Research Service for locating, testing, and obtaining permission to introduce biological weed control agents into the United States. Information is provided for obtaining permits, selecting release sites, and monitoring the population increase of the weed's natural enemies. Precautions are rendered for avoiding problems in setting up and working a biological weed control program. Most of the noxious weeds in the United States were introduced from foreign countries in a variety of ways. These included 1) exotic seeds contained in ballast soil which was dumped from old wooden ships in North American harbors; 2) exotic seeds mixed with farm seeds carried by early immigrants; 3) seeds that were purposely imported by nurseries for flower gardens, etc., and 4) plants which were deliberately introduced whose products were, at one time in our history, to be used in various businesses, e.g. the wool/sheep industry which used Dyers woad (Isatis tinctoria L.) to dye the wool, and teasel (Dipsacus sylvestris Huds.) to tease the wool. Weeds are plants that are currently undesirable to humanity, or to the animals and/or land over which humankind has stewardship. Their undesirable properties may be physical, (e.g. sharp thorns or spines, tacky seeds, etc.) or chemical (e.g. toxic or irritating saps, oils or latex, etc). Generally, exotic plants arrive at a new location without their native enemies, and are therefore able to reproduce and spread, being limited only by their reproductive potential and anything unfavorable in the new environments. There are many types of organisms that are,natural enemies of plants. These include insects, mites, nematodes, pathogens, wild and domesticated herbivores, birds, humans, and sometimes other plants. Both plants and their natural enemies require similar amounts of the same critical components of the This chapter not subject to U.S. copyright Published 1995 American Chemical Society

Hall and Barry; Biorational Pest Control Agents ACS Symposium Series; American Chemical Society: Washington, DC, 1995.


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ecosystem, i.e. temperature, moisture, nutrients and a niche. Each factor must be available in the proper amount, the proper form, and at the proper time to satisfy each organism's requirements. Variation from the ideal configuration of these factors, while possibly not life threatening, may not allow the organism to attain its full potential. Biological control is the utilization of living organisms (natural enemies) to depress the population of a specific organism which is a pest to society. The definition implies that society provides an effort to manipulate (alter) one or more existing element(s) of the environment to thus provide the advantage to the beneficial species. Generally, more than one species of natural enemy is needed to reduce the pest's population to levels tolerable to society, each one providing some level of detrimental influence to the pest organism. The effect may be obvious, i.e., the pest plant is defoliated, deformed or stunted because of the natural enemy, or subtle, such as is the case when the damage caused by secondary organisms is greater and at a later date than damage caused by the natural enemy. A n example of the latter is where a plant is damaged by insect feeding, and the wound is later infected by a pathogen. Because the majority of the noxious weeds in the United States are exotic, and because most of these exotic weeds are simply members of the plant community in their native lands, the best control methods are often to be found by studying the pest plant in its native surroundings to determine 1) what organisms are associated with it, 2) which of these are natural enemies, and 3) which of these natural enemies might be good candidates for introduction for biological control of the weed in its new environment. This method of control is a form of "Classical Biological Weed Control". The eventual effect that a biological control agent will have on its host plant will be the result of 1) the density of the available host(s) compared to the density of the natural enemy, 2) the suitability of local biotic and abiotic conditions for the natural enemy in relationship to the suitability of those same conditions for the host, 3) the diversity in the way that the plant reproduces, i.e., seeds only, or seeds and vegetative reproduction, 4) the ability of the natural enemy to constantly stress the plant, 5) the ability of the plant to maintain and replace root reserves, and 6) the ability of the plant host to recover from the effects of its natural enemy or enemies. If other species of natural enemies are also utilizing the host plant, the impact of the one species may be enhanced or reduced, depending on how the different natural enemy species interact with each other. Procedures for Establishing Biocontrol of Target Weeds There is a complex procedure in place by the United States Department of Agriculture, Agriculture Research Service for locating, screening, releasing and monitoring biocontrol agents that have been accidently or otherwise introduced into North America, and which have been targeted for study. These procedures are the result of many years of experience to perfect a program that is safe. Every effort is taken to ensure that the host range of each introduced biological weed control species is known, and that these agents are not parasitized or diseased. Because each of the host plants and their complement of natural Hall and Barry; Biorational Pest Control Agents ACS Symposium Series; American Chemical Society: Washington, DC, 1995.

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enemies differ in the amount and diversity of testing they must endure, it is impossible to determine how long each set of tests will take. Nevertheless, the steps of this procedure are as follows: I- Determining the Suitability of the Target Rant for Biological Control Procedures. Quite often, pressure from the public drives the priority as to which target plants will be studied, and budget constraints limit the number of plant species that can be studied. Some pest plants may not appear to be good candidates for study, possibly because 1) the cost of study might far exceed that of the benefits, 2) because so little is known about a pest plant that it does not appear threatening enough to be of concern, or 3) because conflicts of interest exist. For those that can be studied, the native land of the target species is identified and scientists begin to check the literature and to study the life cycle and associations of that plant. Those with few or no North American relative species are usually better candidates than are those with many close relatives. If the plant is difficult to locate, or does not attain the vigor, height or density that it does in North America, then it is considered to be a good candidate. Discovering potential biological weed controlling agents on the plant during the survey also assists in making this decision. BE- Conducting Foreign Survey. Once the target plant is approved for study, a survey in its native land is conducted, and natural enemies which are associated with the target plant are catalogued. The potential agents are reared, identified and tested to determine efficacy. For the United States, this is generally conducted through the USDA, ARS's European Biological Control Laboratory, and/or by the IIBC (International Institute of Biological Control). With the aid of published and unpublished literature, records, observations, etc., the various insect/pathogen species from the survey are evaluated as to being passive feeders, such as bees and butterflies, or as being destructive to the target plant. Those which are destructive are then tested to determine what other plant species they also damage. Those with limited host ranges are potential candidates for additional host specificity testing. m- Conducting Host Specificity Screening. The purpose of conducting host specificity tests is to determine, without testing all plant species, the potential host range of candidate biocontrol agent species by exposing the candidate to a number of representative plant species from a number of plant groups. The plant species tested are selected from a centrifugal (concentric circle) plant matrix which recognizes the target plant species as the center, representatives of other species from the same subgenus located in the first ring surrounding the center, representatives of species from other subgenera but within the same genus located in the next ring, representatives from species of related genera of the same tribe in the next ring, etc., with each additional ring being less related to the target organism. In the next to last outer ring, families of economic or aesthetic value (but generally of no close relationship) are represented. In the


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Hosts of related natural enemies Reps, of econ/ sp. Dec relationships


Reps, of next closest genera Reps, of the same genus Reps, of same subgenus

Target species

figure 1. Centrifigal (concentric circle plant matrix for host specificity studies.

last ring, unrelated plants with biochemical or morphological characteristics in common with the target weed are also included, as are representatives of plants which are known to be attacked by other species related to the bioagent being tested. (Figure 1.) The nature of screening tests depends on the target weed and control agent in question. The degree of specificity which needs to be demonstrated and the level of risk which is acceptable rely on the importance of the weed and the presence of non-target species closely related to it in the location where the weed is to be controlled. In "no-choice" feeding and oviposition tests, (i.e. where the test subject can only eat or starve, and lay eggs on the plant provided to it) agents are isolated as male/female groups in containers (cages), each with a test plant, until the agents either die, feed and/or oviposit. Where the agent remains in the test and dies from apparent starvation without physically damaging the plant or ovipositing on the plant, the plant group is designated as outside the potential host range. Where feeding or oviposition occur, the test continues to determine i f 1) the agents can survive in/on the test plant, 2) deposited eggs hatch, and/or 3) the agents can complete their life cycle in/on the test plant. The test then attempts to determine the degree of detrimental effect which is inflicted on the test plant. If the test species is of little concern, but other members may be, then these should be tested.


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The artificial conditions of these tests can produce abnormal results and sometimes lead to the rejection of agents that are normally host specific under field conditions. Therefore, when possible, out-door cage and/or open-field testing of previously unlikely candidates may be conducted in the native land of the bioagent to yield more accurate results. IV- Petitioning. Petitions are written at the beginning of each of the three investigative phases for introduction of a new weed biological control agents. The first petition requests permission to work on a plant project and the accompanying agents. At this point, it must be shown that the target weed would be a suitable candidate for a biological control program. The second petition requests permission to introduce biological control agents into quarantine for host specificity testing. Then when all testing to determine the host range of each candidate agent has been completed, a third petition is written which contains the results of the tests. Presently, these are written in the form of an Environmental Assessment (EA) which are, in reality, a measurement of risk, or a risk assessment. Multiple copies of the petitions are sent to Plant Pest Quarantine (PPQ), a branch of USDA's Animal and Plant Inspection Service (APHIS). PPQ is that branch of the federal government responsible for issuing permits to transport and release insects into the United States. Associated with PPQ is an interagency group of professionals called the Technical Advisory Group (TAG) which is responsible for advising PPQ as to the accuracy and completeness of the testing. Specific members also insure that the results of the testing concern with the Endangered Species Act (U. S. Fish and Wildlife Service) and the Native Plant Act (National Parks Service) are addressed. T A G may decide that 1) the candidate agent may be dangerous and recommend it not be introduced (generally the scientist is aware of bad results at the end of testing, and i f the data indicates danger, would not write and submit the petition in the first place); 2) that the candidate needs more testing; or 3) that the agent appears safe and recommends that it be introduced. PPQ then considers the advice of T A G , but since T A G is only an advisory group, PPQ is not obligated to follow their recommendations, should they have additional concerns or information. If more testing is required, the petition is returned and the additional data are collected before the petition is resubmitted. If, after careful study, PPQ does decide that all is in order, it then submits the petition for evaluation of the environmental assessment. Failure to pass this examination means that more testing must be completed and the petition resubmitted, but this time possibly in the form of an Environmental Impact Statement (EIS). Approval at this and the previous process will satisfy the remaining requirements and allow a permit to be issued. (2)

V- Obtaining Permission to Make field Releases. Once a petition to introduce a new natural enemy of a plant into the United States has been approved, those


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wishing to be responsible for a release in their own state must complete a form PPQ-526, "Application and Permit to Move Live Plant Pests and Noxious Weeds." This application is also used for any organism that is shipped from state to state. The application is then sent to the Department of Agriculture in that state in which the release is to be made. The form must then be signed by someone in authority and sent to the USDA, APHIS office, PPQ.BATS (Biological Assessment and Taxonomic Support), Federal Building, Room 628, Hyattsville, M D 20782 for processing. When this is signed by PPQ, a copy will be returned to the applicant as an approval record. Generally these permits are valid for three years. VI- Checking All Incoming Shipments. Once approval to introduce a natural enemy has been received by the researcher, collections are made and the agents shipped into a quarantine laboratory in the United States. Here a portion are killed, pinned and sent to a taxonomist (an authority for that group, generally associated with the USDA-ARS Systematic Entomological Laboratory (SEL)) to confirm that the species designation is accurate. At the same time, some insects are sent to an insect pathologist to determine whether or not they contain any parasites or pathogens. If a parasite is discovered, the colony can be reared through one generation to remove the parasites. If a pathogen is detected, two courses are possible. Either the colony can be destroyed and, hopefully, another collection site located which is free from the pathogen, or the colony can be split up and reared in individual containers each containing one male and one female. Deposited eggs are kept under a "parent number" until after the females have ceased laying eggs. The adults are then sacrificed and examined for pathogens. Eggs from contaminated couples are destroyed while eggs from healthy couples are reared. This process continues until the colony is pathogen free. VII- Selecting a Release Site. Several factors are important to the selection of sites for releasing and establishing a biocontrol agent. First, the site should be free from chemical treatments such as insecticides and herbicides, or at the least, free from the future use of these chemicals. The field should also be generally free from grazing animals during the initial establishment of the natural enemy, although grazing by wildlife is often insufficient to threaten the establishing colony. A release of 500 adults of the bioagent where one-half or more are female, is generally a logical number to ensure that i f the location for release is suitable, the establishment will be successful. The site should contain those elements of the environment which are necessary for the survival of the natural enemy, such as sufficient supply of the target plant, moisture (either dew, standing water, or sufficient moisture in the plant tissue), sufficient moisture so that the target plant does not suffer from moisture stress, sufficient flowering plants for adult nectar feeders, wind breaks for delicate insects, sunny areas for heat loving insects, shrubs and trees for insects that utilize them for protection and for resting during the day, and


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locations that are free from potential parasites and would-be predators such as ants, rodents, insect feeding birds, etc. When temperature and moisture requirements are known or suspected, it is always advantageous to select climatic areas which meet these specifications, especially when making the initial releases. In many cases, however, more desirable areas may be located by determining which factors cause the more rapid increase of the natural enemy. This can be determined by measuring the progress of previous releases. At present, we know only where certain species can survive, and do not know most of their limitations or desirable essentials. It will take time for this to be discovered. Vm- Obtaining Cleared Agents from North American Sources. Before planning any collections of natural enemies in another state for transport or shipment across state boarders, check with your State Department of Agriculture concerning regulations and restrictions on the importation and/or movement of biological weed control agents within or into your State, and whether or not a permit is required. Generally a PPQ-526 permit is required (see Sect. 5). It is the responsibility of the party receiving the natural enemies to obtain any permits, although sometime suppliers do provide this service. In some cases, your weed bureau or cooperative extension agent can provide assistance. These agencies also like to be kept informed and are often willing to work with you on this type of project. Natural weed enemies can be obtained several ways. If one has seen a particular agent before, and is comfortable in recognizing it, the land manager can make the collections. However, make sure that permission is obtained from the land owner who owns the natural enemies before collections are made. Collectors who provide natural enemies for a profit are a source for those who do not wish to collect for themselves. In either circumstance, make sure that the natural enemies that you will release are the proper species, and are disease and parasite free (see Sect. VI). K - Releasing Cleared Agents. When the permit is obtained and the colony has been determined to be the proper species and free from parasites and diseases, it can be released on the target plant in an ecological condition which is believed best for the survival of the natural enemy. Generally 100 to 500 insects per release are sprinkled over an area of at least 150 square meters on the host plant of moderate density. Tall, dense stands of plants sometimes provide undesirable shading, whereas thinner stands allow more movement and better chance for establishment. Releases should be made in areas free from grazing and or general traffic, when possible. Herbicide and insecticide spraying should not be conducted in the immediate area or in areas close enough to allow drift of the spray. The initial release area should be protected for 5 to 10 years. Other sites may not need as much protection i f the initial source is productive. The judgement to use or not to use cages is generally made from a partial understanding of the life habits of the new biological control agent. If



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the agent is a strong flyer, has difficulty finding a mate, or i f the release numbers are extremely low, cages are generally used. Flying insects, for example, require a large, tall cage in which they can conduct flights to attract a mate and visit multiple host plants, while small insects that do not readily disperse by themselves, can be confined in much smaller enclosures. Nevertheless, cages of any size produce what is known as a "cage effect", because there is limited space, there are "walls" in the environment on which to climb which reduces the time spent on or near the host plant, and unnatural and flexible "fissures" which may affect survival of the agent. Therefore, the larger the cage, the better. Cage material may also be an important factor for those agents that spend much time on the cage fabric. For example, metal fabric holds the heat of the sun, and although the temperature within the cage may be acceptable, the metal may be many degrees warmer and thus slowly cook the resting agent. Fiberglass fabric cages can be damaged by chewing insects such as grasshoppers and crickets, although these insects may not be the confined subjects. Saran® fabric cages are excellent, but become discolored and weakened within a few years, depending upon use and care. If you do not own the land on which you plan to conduct biological weed control, release of the natural enemy on any type of land (public or private) must be made with the consent of the land owner. It is often advisable to have an agreement stronger than just a hand shake because once the agents are released, they belong to the land owner. Therefore, a written cooperative agreement is advisable in which you maintain control of the agents, and which would protect the agent from possible chemical spraying, or other cultural practices such as grazing, mowing, plowing, etc., by the land owner. It is also advisable to write these agreements for protection of the land owner, should you leave the gate open, for example, and let his cow out. These agreements can be written for a limited time period, but five years is generally the shortest time needed for a biological control agent to build sufficiently to occupy ample area to survive most natural or chemical disasters. A period of ten years is more logical. X - Documentation of Importations and Releases. Because classical biological control involves the introduction of exotic organisms into the United States, committed scientists keep detailed records of 1) all exotic materials being imported into quarantine facilities, 2) all shipments from quarantine facilities which are for field release or which will be used in laboratory cultures and studies, and 3) the transfers of established introduced bioagent species to new areas of the United States where these agents have not previously occurred. Specific forms are used in this documentation process, including forms for recording quarantine shipments, and for non-quarantine shipments and releases. Voucher specimens are sent for identification and are also retained by the quarantine facilities of agents received into quarantine, and when the agents are removed from quarantine and field released. Voucher specimens are also retained by various agencies and universities when transferring an agent from


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one location to another. These voucher specimens provide samples for identity verification, should the need arise, and for later taxonomic studies. Nonquarantine personnel involved in releases or recolonization of introduced biological control agents are asked to help document the dispersal of the agents by use of the forms or by providing pertinent data to the scientist evaluating the biological control program. These forms are the AD-943 which can be obtained from, and copies of which should, when completed, be sent to U S D A ARS-BA-IBL, Biological Control Documentation Center, Insect Biocontrol Laboratory, Bldg 004, Rm. 3, BARC-West, Beltsville, M D 20705. (1) XI- Monitoring Release Sites. Once a biological control agent has been released, it becomes necessary to answer the question, "what's happening out there?" We begin to wonder "did the agent become established?"; "are its numbers increasing or declining?"; "is this species acting as expected in its effect on the pest?"; " is the population of the pest increasing or declining?"; " what are the biotic and abiotic forces acting on the bioagent?"; " what effect are these forces having on the newly released bioagent"?; and "how does the agent interrelate with other established organisms?" The most convenient method of answering these questions is to sample the locality to determine how the populations of the biocontrol agent and the target pest change, and in some cases, to observe the amount and type of damage actually inflicted on the target host. The best method of sampling depends on 1) how the agent utilizes its host, 2) the suspected density of the agent at the time of sampling, 3) the life cycle of both agent and host, 4) the desired accuracy of the data to be obtained, and 5) the amount of effort, labor and money which can be expended on taking the samples. Monitoring can be conducted in three ways: The sampler 1) actively samples the study area, 2) uses traps with attractants to catch the desired species, or 3) employs traps which indiscriminately collects insects, mites, spiders, tics, nematodes, etc. I-Examples of active sampling by the sampler. Observation. Probably the "laziest" and often the least statistically reliable method of sampling, observation provides limited estimates. It reveals: 1) that both the target organism and the agent are present, 2) what the agent is doing during the time that it is being observed, 3) the type and amount of damage inflicted on the host, and 4) how this damage has physically affected the host. Since at least one stage of the insect's life is exposed on the plant or outside an insect host, one can easily verify the presence of the agent i f the observation is made during this period of the insect's life cycle. As such, the densities cannot be calculate of the bioagent or host, the area occupied, or what the agent does in those hours when the observer is absent. A better method for obtaining specific data combines observations within a defined boundary, such as rings of a known size, or staked out plots, and counts all of the specimens of a particular species in that given area. Of course the process must be repeated many times, then one can statistically utilize the data. Additional information can be obtained i f one describes about


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what is happening on the stem, leaves, flowers, etc. of that plant, and the soil surface. This should be recorded along with time of day that counts were taken, approximate air and ground temperatures, absence of or approximate velocity of wind, direct sun or shade, moisture conditions, plant density and conditions, etc., presence or absence of the host, etc. If sufficient samples have been taken, one can usually determine if the target species is bunched or uniform throughout the area, and what type of conditions appeared to be favored within the ecosystem. Daubenmyer/Sing Samples. When specific areas are to be sampled with exact results needed, squares, rectangles or rings of known area can be used. Daubenmyer plant sampling frames of specific size can be placed on the ground and all plant material within counted, measured, identified, clipped, sorted and/or weighed to determine the plant composition, canopy cover and biomass of the area. Multiple samples on a periodical basis over an extended area will provide data as to shifts in plant densities, plant composition, etc. Therefore, all samples where the exact sample area, time, conditions, etc. are known, can be statistically analyzed with a high degree of accuracy. The results will provide a reliable record of actual happenings. Rings are often used to count the number of insects, such as grasshoppers, in a given area. If the insects are large enough to be obvious from a distance, then the number of insects is adjusted for the number that enter or leave during the period of observation. The resultant figure is the number of insects for that size sample, with numerous samples providing an average or mean for the area. If insects are too small to distinguish as one approaches, close counting of the insect or other organism within the ring, or enclosing the ring area in a screen and collecting all material therein, can provide the number of insects of the desired species per given area. Paired samples of treated areas versus untreated controls provide data showing the effect of particular treatments. Radial sampling with time at predetermined distances from a release point provides data as to the rate of population expansion for gregarious insects that move out gradually from a release point.. Sweep Net Sampling. Similar to observations, sweep net sampling is conducted when the agent is attracted to, or is in the vicinity of the host. With weed agents, this period is generally restricted to intervals when the agent is feeding on the flowers, leaves or stems, or when the adult agent is attempting to lay eggs. With insects, the agents are most frequent in the vicinity of the prey/hosts when they are feeding or attempting to parasitize the target organism. Therefore, one must be familiar with the natural agent-host association and phenology. Sweep net sampling can be somewhat quantitative but should be done by the same individual at all times and in the same manner because each person has his own style of sweeping. Otherwise the results are generally a reflection of the collecting ability of each sweeper instead of actual variation in the population of the agent. Sweeping can be measured on the number of


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sweeps or the period of time sweeping. Amount and type of vegetation, excitability of the target organism, aspect of the terrain, air and ground temperature, and velocity of wind will all influence the number of organisms collected. Standardization of results can be made by comparing number of insects swept per given area with other numbers of insects observed or collected per given area by more precise means. Dissection. When bioagents or parasites work within the host, both plant and insect host material can be collected and dissected. This provides information as to 1) the infestation or infection rate of the host population, 2) the number of agents per given host, 3) stage of development of both agent and host, 4) species composition of agents when numerous agents are involved, 5) location within the host where the agent resides, and 6) the amount of damage being inflicted by the agents. If the sample size is sufficient, data will provide very accurate indications of the true agent and host population in the surrounding territory. Suction or Vacuum. Gasoline powered engines can provide power for vacuums in the field to collect live insects, spiders and mites from plants. However, unless all plant material is strongly agitated in the suction area, and the soil area also vacuumed, many specimens may be missed. Some species are very difficult to dislodge from debris and vegetation. Therefore, this is frequently not a reliable method to determine density unless the vegetation is checked afterwards to confirm that all organisms have been collected. Vacuums are also used to catch flying insects, but the height of the vacuum mouth and time of day will determine which species may be obtained. Before and After Photographs. This is one of the simplest methods for recording results when working with biocontrol agents of weeds, but is useless when attempting to measure numbers of insect bioagents. Photographic records from consecutive years, taken at approximately the same time each year from the same location and of the same horizon, may be compared to determine the gradual change in the plant community. This method does not provide information as to density of the target host, density of the biological control agent, type of damage inflicted on the target host, etc., but does display the conditions at the time of the photograph. Unlike memory, the photographic records are undeviating and display dramatic, visual differences which generally have a greater impact on an audience than do dry figures and tables. Digging. Often, various stages of arthropods, nematodes, and fungi can be located in the soil or on the root system of the target organism. Depending on the size of the organism being sought, various mesh screens can be used to sift the soil and expose the desired material, water can sometimes be used to float the specimens. Berlese funnels can drive the organisms into collecting traps, and dissections of the root material of the target plant can reveal the bioagent in its natural surroundings.


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Berlese Funnel. These are funnels with a heat source at the top which causes the soil inhabiting organisms to try to escape the heat. They are driven through the screen mesh or wire mesh material which is holding the soil, and falls through the funnel into a collecting container where it is generally killed. This is effective in collecting most soil inhabiting organisms including arthropods such as mites, spiders, insects, scorpions, etc. Water Sorting. Sampling for mites, nematodes and other small worms is often done by dissolving small soil samples in water and checking the fluid under a microscope. By knowing the volume of soil washed and the number of organisms obtained, one can calculate the density of the population. Often samples are taken at continuous levels to determine at what depth in the soil profile the species is most concentrated II- Examples of attractant traps are as follows. Black Light Black light traps are commonly used for attracting flying insects. Not all types of insects will be attracted to the light, because not all species see the same wave lengths of light. Moths and butterflies, flies, some beetles, lacewings, etc. are most often collected. The black light is generally operated at night, and sometimes in the twilight periods. For those species which are attracted to black light, material can be collected from long distances. Insects fly into the baffles, fall into the funnel and are collected in the lower trap which either kills them with chemicals or cold, or holds them until they can be collected. A black light against a bed sheet is sometimes used to attract specimens which are then hand collected. Either method is often used to see what is in the vicinity. However, unless much testing has determined the ratio of collected organisms to those available per given area in the field, this method is not quantitative. Pheromone. These are attractants, or odors which are most often species specific. Usually, they are sex attractants and lure only males or females. If one can calculate the amount of area that the pheromone covers, one can sometimes determine the approximate density of a population. Only minute quantities of material are needed which is carried for great distances on the breeze. This method can attract insects into cages where they can be livetrapped without harm. Sound. This method of attracting insects can also be used to determine the approximate density of a population i f the organism can be attracted by sound and i f one knows the area covered by the sound. Otherwise, like all other attractants, it only shows that there is something in the area at the time sampled. Sound is probably the least used sampling method and is generally very host specific. This method can be used for collecting live material without having to handle it.


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Entrance Traps. These are screen traps with a passage which allows the organism to enter, but the portal is difficult to locate when it wishes to leave. These traps are often provided with some type of food attractant. m- Indiscriminate Sampling. Pitfall Traps. These are commonly cans, glass jars, or some other type of container which can be buried with the opening flush with the soil surface, and which can hold chemicals for killing the specimens. Because the preserving fluid can often evaporate and there is generally a long period of time between visits, regular antifreeze is often used. This method collects arthropods running or walking on the ground, some flying insects attracted to the sweet smell, and in some cases, small rodents. Moths, butterflies and some flies are often difficult to identify after being trapped in antifreeze, but most specimens are quite pliable even days after dying. Again, this is a general method of collecting organisms and does not provide an accurate indication of the density of most species. Sticky Traps. These are similar to the old sticky fly traps. A strip or board is covered with a non-drying sticky material and left in the vicinity of the species one wishes to collect. Sometimes a food attractant, such as sugar, is added, or a bright yellow or orange color is used which attracts many flying species. The main problem here is that i f proper species identification is to be made, one must clean the specimens which generally proves to be a very difficult and time consuming process. XII- Redistribution. When a natural enemy of a target weed becomes established and increases in numbers so as to be easily collected, it is often advisable to redistribute the colony to new locations, especially when they do not appear to easily disperse themselves. This will provide new habitats in which to survive, and generally reduces the likelihood that the colony can be lost, should a local disaster strike the original release location. Collection of material can be made several ways, depending upon the species involved. Sweep nets are generally the most effective, along with black lights, collection and rearing from galls, hand picking of individuals, etc. In any event, collections should be made so as to cause the agent a minimum of discomfort and stress, and captivity should be kept to a period as short as possible. The longer the period of time that an insect is kept, the more eggs that the female will deposit in the container, leaving fewer eggs for the new establishment. Therefore, paraphrasing an old phrase, "time are eggs, and eggs are money". Collections can be made by the party desiring the agents, or by collectors wishing to make a profit. The Federal Agency which is responsible for redistribution of bioagents is APHIS (Animal & Plant Health Inspection Service). APHIS generally creates nurseries for increasing insect numbers, and eventually turns the nurseries over to state agencies after a period of time. As noted above, such redistribution, or recolonization, of introduced biological control agents should be documented, i f such distribution is a



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significant distance from the area from which the collections are made, e.g., more than 25 miles, and particularly, i f distribution is made to another County or State. The USD A Biological Shipment Record - Non-Quarantine (Form AD-943) is available for use for such shipments or recolonization, if desired, or otherwise indicates the kind of information that should be recorded and provided to the scientist(s) responsible for evaluating the particular biological control program. Supplies of the form are available from the responsible research scientist(s), APHIS, or USDA-ARS-BA-IBL, Biological Control Documentation Center, Insect Biocontrol Laboratory, Bldg 004, Rm. 3, B A R C West, Beltsville, M D 20705. (Coulson, 1992) Caution: Make sure that all insects to be transferred to the new location are the proper species. If any question exists, have all insects checked by an experienced entomologist or the SEL (Systematic Entomology Laboratory, USDA, ARS, Center-West, 10300 Baltimore Ave., Room 101 A , Bldg 046, Beltsville, M D 20705-2350: Ph. (301) 504-7041) before they are released. It is also advisable to have insects being transported over long distances checked by an insect pathologist to insure that the colony that is being transferred is clean, and will not be hindered by its own controlling agents, such as parasites or pathogens. After making collections, insects should be sorted from other species, counted and stored in containers or cages which will allow them to move about and feed on their host plant until time of transport or shipment. In cool storage, many natural enemies can be stored for several weeks i f they are provided with intermittent periods of warm temperatures to allowed feeding and move about. However, it is best to ship or transfer quickly and release insects as soon as possible after collection to enable them to deposit most of their eggs at the release site rather than in the carton or cage. The best containers are tight cardboard or paper cans, such as the old style ice cream cartons. Plastic or glass cartons are not recommended because they allow moisture to build up, which increases insect mortality. Shipment should last no longer than several days, because eggs are laid in the container when the natural enemies warm up, and ice packs generally only last 12 to 24 hours. For travel, the insects should be transferred to containers which include part of the host plant for food, and as something on which to hold. Lids should be taped around the edges to prevent escape. Do not ship parts of the plant which might reproduce at the new location, such as root material or seed. The cartons containing insects and fresh plant material can then be stored in refrigerators at temperatures safe to store lettuce until shipment/transfer or in cool ice chests during shipment/transfer. Make sure that cartons and ice packs are not loose but firm within the shipping containers. XII- What You Should and Should Not Do. The successes of many biological weed control programs have made the use of natural enemies a desired procedure for many land managers. Through talking with their neighbors, observing before and after photographs of the effects of the bioagent on a patch



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of the host plant, observing first hand these effects on field trips, reading and listening to news releases and articles, and then considering their weed control costs, they have been sold on the effectiveness biological weed control in solving some of their problems. Therefore, They want some of these natural enemies, and THEY WANT THEM NOWl The forces which sometimes cause a frenzy to obtain biological weed control agents are many but are interrelated. These include 1) weed laws and the pressures for their compliance, 2) an awareness that there is a major weed problem, 3) the need for proper land management, 4) the costs of chemical and other types of control, 5) reduction of grazing, farming and recreational areas due to the presence of the weed, 6) reduced productivity, and 7) now and then the loss or injury of livestock. There are many other types of control methods, ie., chemical, mechanical, cultural and integrated. However, biological control is by far the least expensive overall because once established, the natural enemies are self perpetuating. It is at this point that problems can arise i f proper precautions are not taken, especially i f the land manager rushes blindly into a bio weed control program without understanding what is happening, and without the proper education. The most apparent problems are obvious. By blindly ordering agents without knowing what is needed, or under what conditions each agent species does best, one can waste money on the wrong agents, or release the correct agents in areas where they may not survive. By not checking the weeds to see i f the natural enemies are already in the area, one may purchase and release a minute number on top of a large number of agents that are already established, and money is wasted. By purchasing agents that have not been tested for pathogens or parasites, one can release biocontrol agents of the biocontrol agents that they need. Again, money is wasted. If the bioagent is not properly identified, one might receive an organism that appears very similar to the natural enemy, but one that has a completely different food range. Again, money is wasted. In this case, not only is the money lost that purchased the erroneous agents, but more money will be needed to control the introduced pest. More important, the land manager may not realize the mix up and will blame the bioagent. This hurts the concept of biocontrol for that land manager. The best way to avoid problems is to take the following precautions. 1). Become educated on what biological weed control is, how it works, which natural enemies will work best on your weed, which of these agents will work best under your land management and environmental conditions, how to integrate biocontrol into your land management practices, how to monitor the progression of the natural enemy build up and its impact on the weed, and how to insure that you obtain the proper, healthy species of agent. Much of this information can be obtained through and from local weed control departments, state and federal departments of Agriculture, some areas of the Bureau of Land Management, Forest Service, BIA, USDA-APHIS and the USDA-ARS Rangeland Weeds & Cereal Research Unit, in Bozeman, MT.



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2) . Work with personnel from your local weed control department They need to be informed of where bioagents are located to protect them from potential spray programs, and in some cases, be able to report to the State department of agriculture that the program is operating in your area. They can also be of great assistance in supplying you with update information, and helping to make your integrated program work. 3) . Obtain a statement through the supplier (when purchasing weed natural enemies) from a reliable taxonomist, on the authenticity of the agent, and a report from a reliable insect pathologist that the colony that you receive is disease and parasite free. If you collect the agents yourself, send a sample of your collection to a reliable taxonomist and another sample to a reliable insect pathologist before making a release. 4) . Select the best natural enemy or enemies for your environmental area, and the best areas on your property which meet the requirements of the natural enemy, and exclude that area from grazing, spray programs, and general disturbance for a period of at least 5 to 10 years. To avoid duplication, make sure before you obtain the new agents that the natural enemy has not already found your patch of weeds. From this core, the agents can increase in number and area occupied, and eventually will migrate to those weed infested areas outside the exclosure. Also, from this nursery, and when numbers warrant (generally after 3 or 4 years), collections can be made for releases at areas distant from the establishment. Removal of these "starter colonies" at this time should not noticeably diminish the effect of the established colony. 5) . Treat your weed's natural enemies like livestock, because they are. Each species has its own living requirements as to the temperature range within which it can endure, its moisture requirements, the ecological nitch within which it can survive and flourish, and the type of food that it needs. Insects, for example, are animals which differ from cows and sheep only by three conditions; 1) size, 2) three pair of legs rather than two, and 3) the fact that they wear their skeleton on the outside rather than on the inside. Mites differ from insects in the number of legs (4 pair), and nematodes are missing both legs and an exoskeleton. Pathogens are a different type of organism, but provide the same end result with the same level of safety. 6) . Do not halt normal weed control programs (including chemical control) outside the areas occupied by the weed's natural enemies while you are waiting for biocontrol to work. Rather, determine each year how far out from the center the colony has progressed, and after calculating a buffer zone, continue the programs. Although the numbers of the bioagent should greatly increase each year, it is more difficult for the population of the agent to "catch up" to that of the weed if the weed is allowed to continue its yearly unrestricted increase. 7) . Take photographs of the colony site at the same time each year from the same location and with the same horizon in the photograph. Although all of us have good minds, we sometimes forget how bad the weed problems were in years past i f we do not have some type of record to remind us. These photographs will display how extensive the weed infestation was, and how


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prominent is the impact each year by the bioagents. It also provides justification for your expenditures in time, effort and money. The use of natural enemies to take care of your weed problem can be a very rewarding experience i f it is done correctly. It is a tool to be incorporated with other weed control and land management practices. It requires much knowledge, as does other facets of ranching and farming, and sometimes as much effort to make it successful.. X I V - The Potential of Biological Weed Control. We now have sufficient knowledge to know that the science of biological weed control is still in the very early stages. However, we are now beginning to understand the basics of how the interactions and interrelationships influence the survival of various organisms, and how these processes can be manipulated to benefit one organism or another. Concepts of biological weed control are constantly being revised as new knowledge becomes available. Recent concepts which provided possible solutions actually were in conflict with each other. For example, we thought that as natural enemies lived at the expense of their hosts, sufficient hosts would be allowed to survive so as to continue the livelihood of the natural enemies. If one examines this concept closely, one can see that it suggests that there is some thinking on the part of the natural enemies that would purposely allow some plants to survive, or restrict their own population. Now we perceive a different circumstance. When a new species of organism has evolved through mutation, and that organism is able to reproduce and survive, it carries with it a full compliment of genetic parameters that determine within what temperature ranges, moisture ranges, host or food ranges, niche ranges, etc. it can survive. Plants are producers and thus utilize the soils, being restricted in the area they occupy by temperature, moisture and soil extremes. The environment in relation to the genetic parameters of that species determines how far north and south this species will survive (in conjunction with the elevation), while oceans provide the east-west boundaries, and can provide north and south boundaries i f the genetic potential exceeds the environmental limits and available land area. New and existing natural enemies also have their own genetic constraints which determine where or how they can survive. In some areas, the plant and natural enemy relationships are overlapping, in others they nearly duplicate. Therefore, the plant's natural enemy can live in an environment which is genetically acceptable, and feed, grow and reproduce, being limited only by its own potential and any unfavorable forces in that environment. If the environment favors the natural enemy, it is then possible that the natural enemy may completely remove all of its host from that part of the environment and be forced to live with its host in those areas where the environment is more favorable for the host's survival. This is what has happened in the native lands of those exotic plants that have since become our weeds With classical biological control, our aim in not to control weeds through black magic as some think, but to recreate that


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balance of nature that is normal in the introduced weed's homeland. With the proper balance of natural enemies, these weeds may someday become as difficult to find in the United States as they are in their native land(s). Literature Cited (1) Coulson, J. R.; Crop Prot. 1992, 11:195-205. (2) Coulson, J. R.; Soper, R. S.; Williams, D. W. (ed); Appendix 3: 151-194. In Biological Control Quarantine: Needs and Procedures. Proceedings of a Workshop. USDA, ARS; 1991, ARS-99:336 pp. January 12, 1995


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Biological Weed Control Technology - ACS Symposium Series (ACS

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